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Fish consumption in the Great Lakes

Fish consumption
    in the Great Lakes

Fish | Breast milk | Fish consumption advisories
Critical contaminants | Reducing exposure

Critical contaminants in fish
Many chemical contaminants are present in surface waters at very low concentrations. Some of these chemicals can bioaccumulate in aquatic organisms via their diet and become concentrated at levels that are much higher than in the water itself. This is especially true for substances that do not break down readily in the environment, such as persistent chemicals - like toxaphene and PCBs. In the process of feeding, these persistent chemicals are collected.

Small fish and zooplankton eat large quantities of phytoplankton. In doing so, any toxic chemicals accumulated by the phytoplankton are further concentrated in the bodies of the animals that eat them. This is repeated at each step in the food chain. The concentration of some chemicals in the tissues of top predators, such as lake trout and large salmon, can be millions of times higher than the concentration in the water. Although bioaccumulative chemicals are present in other food, the concentrations that build up in fish, due to the number of steps in the food chain of fish, are much higher than in other food.

All foods, including fish, contain environmental contaminants. Federal government agencies restrict the sale of fish based on environmental contaminants in the edible portion. When setting the acceptable level of a contaminant in commercial fish, federal governments take into account several factors in addition to potential health effects including: assumptions about how much fish people eat, the species consumed, where the fish come from, and economic considerations.

State and provincial governments provide information to consumers regarding consumption of sport-caught fish. This information is not regulatory -- it is meant for use as guidance, or advice. Although some states use the federal commercial-fish guidelines for the acceptable level of contaminants when giving advice for eating sport caught fish, consumption advice offered by most agencies is based on human health risk. This approach involves interpretation of studies of health effects from exposure to contaminants. Each state or province is responsible for developing fish advisories for protecting the public from pollutants in fish and tailoring this advice to meet the health needs of its citizens. As a result, the advice from state and provincial programs is sometimes different for the same lake and species within that lake.

The toxic endpoints used in risk assessments for calculating safe fish consumption levels are subtle (the effects are not easily recognizable or attributable to a particular exposure and that exposure does not cause immediate harm). Numbness of fingertips, dizziness, and the sensory loss that might occur from toxic exposures to methylmercury, might also easily be attributed to the normal aging process. Developmental problems resulting from in utero exposure to PCBs are difficult to measure or even separate from confounding factors like smoking or alcohol consumption. The variability in response of individuals exposed to persistent bioaccumulative toxic (PBT) chemicals dictates a more conservative approach, perhaps producing guidance that is over protective of a large portion of the population.

It is important that people are aware of contaminants in fish and the actions that can be taken to reduce exposure, particularly those people who are at greatest risk from those exposures from overexposure to contaminants found in fish. Exposure to detrimental levels of environmental contaminants can cause a variety of negative health effects. The precise level of contaminant exposure that is detrimental to an individual is going to vary with his/her age, sex, genetics, current physical condition, and previous exposure of that individual. Individuals within a population will vary in their sensitivities to environmental contaminants. It is not possible to determine a priori which individuals within a population are going to be most sensitive to contaminant exposure. Because governments need to protect sensitive individuals in the population, the advice governments provide may be over protective for some portion of the population.

While the average person in the Great Lakes basin may not be at risk of experiencing adverse health effects from exposure to contaminants through the consumption of fish, there are some people who are at risk. These include people who eat a lot of Great Lakes fish, regularly eat large predator fish, eat fish from highly contaminated waters, or eat a large amount of fish over a short period of time. In addition, the developing fetus and young children are at greater risk than adults.

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